An engine appropriately mixes air and fuel and generates driving power by burning the mixed gases. In order to obtain a required, or desired, output of power and combustion efficiency, sufficient air should be supplied to the engine. For this, a turbocharger is used to increase combustion efficiency and supply sufficient air to the engine.
Generally, a turbine of the turbocharger is rotated by pressure of exhaust gas exhausted from the engine, a compressor of the turbocharger compresses fresh air flowing in from the outside, and the compressed air is supplied to a cylinder of the engine. The turbocharger has been applied to diesel engines, and has recently been applied to gasoline engines.
As another example, an electric supercharger compresses external air using a compressor operated by a motor. Since the electric supercharger is operated by the motor, there is little or no turbo lag. The electric supercharger mainly supplies compressed air to the cylinder in a low speed and low load region.
Generally, the turbocharger (hereinafter referred to as a ‘mechanical turbocharger’) operated by exhaust gas may have low responsiveness, and there is a problem in realizing an engine having a high compression ratio because of high back pressure. Also, since the turbocharger is exposed to high temperature exhaust gas (i.e., Celsius 700 degrees), design costs of peripheral parts of the turbocharger is increased.
Further, since the output power of the motor is limited according to an output of a battery provided in a vehicle, the usage of the electric supercharger is limited to a low and middle speed region.
Therefore, there is a demand for a new engine system having the mechanical turbocharger and the electric supercharger.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.